1. Field of the Invention
The present invention relates to a method and apparatus for forming images on both sides of a sheet corresponding to images on two sides of an original.
In the present invention, known image formation processes such as electrostatic recording methods or electrophotographic processes may be adopted. Furthermore, in accordance with the present invention, the material of the original or a sheet is not limited to paper but may be a resin such as a plastic or a metal. The present invention is not limited to an electrophotographic copying machine and can be applied to known image formation apparatuses such as laser beam printers or image recording apparatuses. In the present invention, the method of reading an image of the original is not limited to one wherein the original surface is exposed and an image of reflected light is directly guided. For example, known methods may be adopted including a method of converting image information into an electrical signal.
2. Description of the Prior Art
An example of an electronic copying machine will be described below.
In a conventional machine, in a mode for preparing a plurality of sets of sheets with images copied on both surfaces thereof corresponding to images on a set of a plurality of the originals each having images on the two sides thereof, the copy sequence and the circulation order of the originals are performed by the following first and second methods:
(a) First Method
According to this method, copying of images on two sides of sheets is performed one by one for each of a set of a plurality of the originals having images on two sides thereof. To describe an example, in order to perform two-side copy of a set of 5 originals (10 pages), the fifth original is fed from an original table onto an original glass table so as to copy the image of the 10th page on the first side of the sheet. The same sheet is reversed and is fed again onto the original glass table to copy the image of the 9th page on the second side of the sheet. Thus, the copying operation for the fifth original is completed. The original is reversed again and is returned to the original table. The same operation is repeated for the fourth to the first originals so as to produce a set of five copies corresponding to the five originals. In order to obtain a plurality of sets of such five copies, the entire copy cycle is performed a required number of times.
This method allows sequential two-side copy for each of the originals to be copied. Therefore, this method is effective when the number of sheets is small. However, when the number of sheets is increased, the copying time is increased. Furthermore, the number of reversal of the originals is 2n.times.m where n is the number of the two-side originals and m is the number of sets of copies to be produced. If a sheet reversing mechanism is included at the side of a copying machine, the total number of reversal of the originals can be decreased to half, i.e., n.times.m. However, since this technique is not directly related to the present invention, it will not be described here. In any case, this method has a problem of slow operation as described above. In addition, since the originals are reversed a number of times, the originals are subject to damage. If an automatic recycle draft feeder (RDF) is used, it must have an automatic original reversing mechanism, resulting in a large and complex system.
(b) Second Method
According to this method, even pages (or odd pages) of a set of two-side originals are copied. The even page copied sheets are stored in an intermediate tray. Thereafter, the odd pages of the originals are sequentially copied on the other side of the corresponding copies. When this method is described with reference to the same case of a set of 5 two-side originals, the fifth original is fed from the original table onto the original glass table to copy the image of the 10th page. Then, the original is reversed and is returned to the original glass table. After that, the fourth original is fed and the image of the 8th page is copied. Subsequently, the images on the 6th, 4th and 2nd pages of the third to the first originals are copied. The copies of even pages are all stored in the intermediate tray. The respective originals are reversed, and are returned to the original table. The fifth original which has been reversed and stored is fed onto the original glass table so as to copy the image on the 9th page onto the second side of the copy having the first side on which the image of the 10th page is copied. The original is reversed and is returned to the original table. Likewise, the copy operations of the 7th, 5th, 3rd and 1st pages are performed on the second sides of the copies each having the first side with the respective even page image. In this manner, a set of five two-side copies corresponding to the originals is produced.
In this method, since the originals are all reversed and are returned, when the copy cycle is completed, all the originals have been returned onto the original table in the same order as prior to the copying cycle. When a plurality of sets of copies must be produced, the above operations are repeated a required number of times.
FIG. 1 is a flow chart showing the relationship between the originals and sheets for performing the two-side copy by the second method. The originals O.sub.1 to O.sub.5 are placed on the original table to increase in page number downward, as shown in FIG. 2A. The originals stacked in this manner are sequentially supplied onto the original glass table from the lowermost original O.sub.5. The original O.sub.5 is passed along the glass table without performing exposure and is conveyed into an original return sheet path mechanism. After a switch back sheet path, the original is reversed and is returned onto the original table again. When this operation is performed once for all of the originals, the originals O.sub.1 to O.sub.5 are now in the order as shown in FIG. 2B. Then, when the lowermost original is fed onto the original glass table, the 10th page (even page) as the final page faces the original glass table. When the copy operation for the 10th page is completed, the sheet (on one side of which an image is copied) is stored in the intermediate tray. After the exposure operation is completed, the original is reversed and is returned onto the original table. When this operation is performed once for each of the originals, five copies P' each having even page image copied on the first side are stacked in the order as shown in FIG. 3A. The originals have been returned onto the original table 2 in the order as shown in FIG. 2A. When the originals are then supplied from the lowermost one onto the original glass table, the 9th page as the last page among the odd pages faces the original glass table. The image on the 9th page is copied on the lowermost sheet fed from the intermediate tray, that is, on the second side of the sheet having the image of the 10th page formed on one side thereof. The copy sheet obtained (a two-side copy of 9th and 10th pages of the original) is discharged. When this operation is performed for a full cycle (until all the copies P' in the intermediate tray are fed), a set of 5 two-side copies P" are stacked in the page order as shown in FIG. 3C. Meanwhile, the originals have been returned onto the original table in the page order as shown in FIG. 2B.
When the above operation is repeated the number of times corresponding to the number of sets of copies to be required, a required or ordered number of sets of two-side copies can be produced.
According to this second method, the copying time can be shortened as compared to the first method. However, the number of reversal of the originals in the case described above is at least 2 n.times.m where n is the number of two-side originals to be copies and m is the number of sets of n copies to be produced.
When the last set of copies is produced in the case described above, the originals on the original table are in the state as shown in FIG. 2B. Therefore, the originals must be fed again to return the page order to that shown in FIG. 2A. However, when the originals are returned after exposure of the final odd H) pages without reversal, this final reversal operation can be omitted.
Also, if a sheet reversing mechanism is included at the side of a copying machine, the total number of reversal of the originals can be decreased to half i.e., n.times.m.
In the case according to the second method, the number of reversal of the originals is also many, and the originals may be jammed or damaged frequently. An automatic recycle original feeder must be used together with an automatic reversing mechanism, also resulting in a large and complex system.
Although the first and the second methods each are described with the single example above, various different procedures are known with respect to the page order (from smaller or larger pages, from even pages or odd pages, etc,) or the reversal positions of the originals.